As a method of producing an optically active 2-methylpiperazine, for example, a method is known in which (±)-2-methylpiperazine is optically resolved with an optically active tartaric acid; or a method in which (±)-2-methylpiperazine is optically resolved with an optically active 2-phenoxypropionic acid. Further, as a method of isolating an optically active 2-methylpiperazine from the salt of the optically active 2-methylpiperazine with an optical resolution agent, obtained by the optical resolution, a method is known in which the optically active 2-methylpiperazine is separated by distillation; or a method in which the optically active 2-methylpiperazine is isolated as a mineral acid salt. In addition, as a method of isolating an optically active 2-methylpiperazine from the mineral acid salt of the optically active 2-methylpiperazine, a method is known in which the mineral acid salt is reacted with an alkali metal alkoxide in a lower alcohol, and after filtering the resulting solution and concentrating the filtrate, the crystal is crystallized (See, JP 2004-161749 A and JP 2002-332277 A).
However, since the optically active 2-methylpiperazine obtained by distillation has a high melting point of from 91 to 93° C., the optically active 2-methylpiperazine obtained by those methods solidifies at room temperature. Therefore, when the thus obtained optically active 2-methylpiperazine is used, for example, when it is weighed, dissolved, transferred or the like, it is necessary to heat and dissolve the 2-methylpiperazine, making it difficult to handle.
The problems associated with the optically active 2-methylpiperazine isolated by distillation can be solved, by using a method in which, after collecting the optically active 2-methylpiperazine as a mineral acid salt, the mineral acid salt of the optically active 2-methylpiperazine is reacted with an alkali metal alkoxide, and then the liberated optically active 2-methylpiperazine is crystallized, to obtain the 2-methylpiperazine as crystals, because the resulting optically active 2-methylpiperazine can be handled as crystals. However, since that method includes a step of forming the mineral acid salt of the optically active 2-methylpiperazine, it results in a longer production process. Further, when the salt is decomposed with an alkali metal alkoxide in an alcohol solvent, an excess amount of alkali metal alkoxide and/or inorganic salt is/are dissolved and mixed into the solution of the liberated optically active 2-methylpiperazine. Accordingly, a step of removing impurities such as the excess amount of alkali metal alkoxide and/or inorganic salt is required, thereby complicating the operation.
As described above, no industrially applicable method has been known which is capable of producing an optically active 2-methylpiperazine having a good handleability and favorable properties. Accordingly, there has been a demand to find an industrially applicable method that produces an optically active 2-methylpiperazine having a good handleability and favorable properties.
It could therefore be helpful to provide a method capable of industrially producing an optically active 2-methylpiperazine having a good handleability and favorable properties, with a short production process.